Ultrasound application devices are known for use in physiotherapy, e.g. for pain reduction but also for anti-stress and wellness therapy. Such devices comprise a hand-held applicator comprising a converter element for converting electric signals into ultrasound waves and a treatment head configured to apply ultrasound waves of the converter element to a subject, or patient, to be treated, as well as an oscillator circuit to generate an electric output signal to drive the converter element and a power source to drive the oscillator circuit.
Typically used ultrasound frequencies range between about 10 mHz to about 3 MHz. Generally, an ultrasound power density or intensity generated at the treatment head between about 0.05 and about 0.4 W/cm2 is considered “low power”, and an ultrasonic power density between about 0.8 to about 3 W/cm2 is considered “high power”. The useful surface area of the treatment head determines the total power deliverable or delivered to the subject and the total power to be delivered by the oscillator circuit to the converter element.
Ultrasound application devices for professional use generally comprise treatment heads with effective surface areas of several cm2, e.g. about 5 cm2. A high power device thus should deliver about 4-15 W ultrasound power. Presently, such powers can only be delivered by two-part devices comprising a power unit and a hand-held applicator coupled with a cable, wherein the power unit comprises the power source and the oscillator circuit, and the hand-held applicator comprises the converter element and the treatment head. The output signal of the oscillator circuit must be transmitted through the cable. Even an efficient oscillator circuit generates heat so that the power unit requires a cooling system; for high power operation several Watts of thermal energy have to be siphoned off to prevent the oscillator circuit from overheating.
EP 0 176 136 discloses an ultrasound application device, which comprises an adjustable element provided in a treatment head, the adjustment of which indicates the efficiency and the impedance of the converter element, and a controlling circuit being provided for influencing the electrical output signal in dependence on the adjustment of the adjustable element in such a manner that the treatment head delivers ultrasound waves with the desired intensity.
Although operating successfully the device and the effort required for adjusting the adjustable element and possible associated recalibration of (portions of) the device are considered complex. A simpler, preferably more energy-efficient, device is therefore desired.
US 2004/0171970 and DE 40 15 686 teach that energy consumption of an ultrasound device may be reduced to a point where the device may comprise an integrated battery-operated hand-held applicator by reducing the ultrasound output power by intermittent interruption of the output power. The effectively delivered ultrasound power over the course of a treatment is thus a fraction of the stated power and intensity. This restricts usability of the devices which is undesirable for professional medical and/or physiotherapeutic practice.
Further, DE 196 24 163 discloses an ultrasound system comprising a compact unit housing the entire therapy system and coupled to the external current supply via a network plug. A microcomputer controls the overall operation of the therapy system.
WO 2004/110558 discloses an ultrasonic skin care device having an applicator head for applying the ultrasound vibrations to a user's skin. The applicator head has a vibrator element and a horn which are integrated into a combined vibration mass that resonates with an electric pulse to produce the ultrasound vibrations. The device is configured to limit the ultrasound upon detection that the applicator head is out of a normal contact with the skin. Consequently, there is a desire for an improved high power ultrasound application device.